Neoplastic lymphocytes of cutaneous T cell lymphoma (CTCL) have T cell features and distinctive tissue distribution. They facilitate or "help" polyclonal B cell differentiation in vitro. Availability of homogeneous populations of monoclonally-derived neoplastic T cells from patients with CTCL and accessibility of infiltrated skin for study provide unique opportunities to correlate cellular features with specific clinical manifestations of the disorder. The proposed studies have three interrelated objectives. (1) To identify tumor and tissue-specific antigens (characteristic of the helper T cells from which the neoplastic T cells have originated), a hybridoma system will be used to produce monoclonally-derived antibodies. (2) The basis of the interaction between the neoplastic cells of CTCL and the skin will be investigated. Studies will be performed using a tissue culture system which permits differentiation and stratification of epidermal cells without requiring growth-supporting cells or agents. Epidermal cell production of chemotactic factors, membrane interactions with T cells and inductive effects on lymphocyte differentiation will be studied. (3) To determine if surface differentiation antigens of CTCL cells can be used to therapeutic advantage, a clinical trial anti-thymocyte globulin will be expanded. Together, these studies are designed to identify the biologic significance and clinical relevance of the special features of the neoplastic cells of CTCL.